I have an 18V Rigid angle grinder ( model R86040 ) that doesn't work so I dismantled it and do not understand what I found. The motor appears to have 4 brushes and the magnets in the stator are so strong that it was difficult to remove the rotor. Have things changed so much since I dismantled my last electric tool? Are 4 brushes common and is it normal to have such strong magnets in the stator?